This invention relates generally to a method and apparatus for necking containers and, more particularly, concerns a solid, expandable pilot member for supporting the interior surface of a two-piece beverage can during a necking operation.
Two-piece cans are the most common type of metal containers used in the beer and beverage industry and also are used for aerosol and food packaging. They are usually formed of aluminum or tin-plated steel. The two-piece can consists of a first cylindrical can body portion having an integral bottom end wall and a second, separately-formed, top end panel portion which, after the can has been filled, is double-seamed thereon to close the open upper end of the container.
An important competitive objective is to reduce the total can weight as much as possible while maintaining its strength and performance in accordance with industry requirements. For pressurized contents such as soft drinks or beer, the end panel must be made of a metal thickness gauge that is on the order of at least twice the thickness of the side wall. Accordingly, to minimize the overall container weight the second end panel should be diametrically as small as possible and yet maintain the structural integrity of the container, the functionality of the end, and also the aesthetically-pleasing appearance of the can.
In the past, containers used for beer and carbonated beverages had an outside diameter of 2{fraction (11/16)} inches (referred to as a 211-container) and were reduced to open end diameters of (a) 2{fraction (9/16)} inches (referred to as a 209-neck) typically in a single-necking operation for a 209 end; or, (b) 2{fraction (7.5/16)} (referred to as a 207xc2xd-neck) typically in a double-necking operation for a 207xc2xd end; or, (c) 2{fraction (9/16)} (referred to as a 206-neck) in a triple- or quad-necking operation.
More recently, the open ends of beverage containers have been necked to 2{fraction (2/16)} (referred to as a 202-neck). The 202-neck is created using ten to sixteen separate, sequential operations. Further, different can fillers use cans with varying neck size. Hence, it is very important for the can manufacturer to quickly adapt its necking machines and operations from one neck size to another.
Years ago, the process used to reduce the open end diameter of two-piece containers to accommodate smaller diameter second end panels typically comprised a die necking operation wherein the open end was sequentially formed by one, two, three or four die-sets to produce respectively a single-, double-, triple- or quad-necked construction. Examples of such proposals are disclosed in U.S. Pat. Nos. 3,687,098; 3,812,896; 3,983,729; 3,995,572; 4,070,888; and 4,519,232. For these patents, it should be noted that in each die necking operation, a very pronounced circumferential-step or rib is formed. This stepped rib arrangement was not considered commercially satisfactory by various beer and beverage marketers because of the limitations on label space and fill capacity.
In an effort to offset the loss of volume or fill capacity resulting from the stepped rib configuration of the container, efforts have been directed towards eliminating some of the steps or ribs in a container neck. Thus, U.S. Pat. No. 4,403,493 discloses a method of necking a container wherein a taper is formed in a first necking operation. A second step or rib neck is then formed between the end of the tapered portion and the reduced cylindrical neck.
U.S. Pat. No. 4,578,007 also discloses a method of necking a container in a multiple necking operation to produce a plurality of ribs. The necked-in portion is then reformed with an external forming roller to eliminate at least some of the ribs and produce a frustoconical portion having a substantially uniform inwardly curving wall section defining the necked-in portion.
However, beer and beverage marketers prefer a neck construction having a relatively smooth neck shape between, for example, the 206 opening and the 211 diameter can. This smooth can neck construction is made by a spin necking process, and apparatus as shown, for example, in U.S. Pat. Nos. 4,058,998 and 4,512,172.
More recently, U.S. Pat. No. 4,774,839 disclosed a die necking apparatus for producing a smooth tapered wall between the container side wall and a reduced diameter neck. The apparatus includes a plurality of rotatable necking turrets, each having a plurality of identical necking substations with a necking die.
The necking dies in the respective turrets include an internal configuration to produce a necked-in portion on the container. The necking substations also have a floating form control element or pilot member that engages the inner surface of the container to control the portion of the container to be necked. The necked-in portion is reformed in each succeeding turret by dies to produce a smooth tapered wall between the arcuate segments without the need for subsequent roll forming.
The pilot member generally does not provide support or guidance from the moment the can edge contacts the die to the moment the can edge contacts the floating pilot member. Consequently, the can edge is susceptible to wrinkling or pleating
One way of overcoming the above problem is to reduce the clearance between the initial can contact with the necking die and the pilot member by increasing the number of necking operations. This is very expensive, however, because each necking operation requires a separate necking station.
Further, even with an increased number of necking operations, small wrinkles may form on or near the open edge of the can. These wrinkles are ironed out during subsequent necking operations by forcing the edge of the can between the cylindrical upper portion of the necking die and the floating pilot member. The ironed out wrinkles create localized regions exhibiting increased work hardening that are generally more brittle than adjacent areas and may fail (i.e. fracture or crack) when the open end is flanged.
Wrinkles become even more prevalent as the container sidewall is down-gauged from approximately 0.0062-0.0064 ins. to 0.0050-0.0054 ins. To avoid wrinkling, four to six additional necking operations may be required. Additional necking operations, however, require additional manufacturing space, pressurized air, electricity, and manufacturing time. Thus, adding additional necking operations is cost prohibitive.
Despite these difficulties, producing a suitable 202-neck container from thinner gauge material remains a manufacturing goal. To produce such a 202-neck container while maintaining the current number of necking stations requires extreme dimensional control of both the necking die and pilot member diameters, and the force required to insert the edge of the can between the necking die and the pilot member tends to crush the body of the can or flatten the bottom of the can. Consequently, the can has to be pressurized to twenty to thirty or more psi prior to forming.
To prevent loss of control of the can edge, the pilot member may be shaped over the entire inside profile of the die. Once the neck is formed, however, the can cannot be removed from the pilot member. Methods have been developed to expand the pilot member during the necking operation to keep the edge of the can in contact with the die and to return the pilot to its original size for can removal.
One such apparatus is disclosed in U.S. Pat. No. 5,755,130. The apparatus includes a pilot having an elastomeric sleeve and a means for providing for lateral deformation of the sleeve. During necking, the sleeve is controllably deformed in a manner such that the lateral portion of the sleeve is placed into supporting engagement with the interior wall of the can, pressing the can against the transition zone of the die. This supporting action of the elastomeric material against the can wall during the reduction in diameter is aimed at avoiding the formation of localized pleats.
Another such apparatus is disclosed in U.S. Pat. No. 6,032,502. The apparatus of this patent includes a die assembly having a cylindrical die for engaging the outer surface of the container and spinning pilot rollers which support the inner diameter of the portion of the container to be necked. The drawback of this method is that the inner surface of the container is only supported at the area where the roller contacts the inner surface.
The present invention provides a rigid, expandable pilot member to eliminate the drawbacks of the current necking apparatuses.
The present invention is directed to a method and apparatus for necking the open end of a container. The method disclosed herein overcomes the difficulties described above by using a rigid, expandable pilot member which provides a continuous surface for supporting interior surface of the container during a die-necking operation.
An object of the invention is to reduce the thickness of the metal at the open end of the container while reducing the diameter of the container""s open end. The apparatus replaces a conventional pilot member with an expandable metallic pilot member.
The expandable pilot member comprises a plurality of segments which are individually expandable to form a continuous surface. In its unexpanded condition, some of the segments are retracted inwardly of other segments. Upon expansion during the necking operation, end portions of the individual segments mate to form a continuous surface. Thus, the entire circumference of the interior wall of the container is supported because there are no gaps between the individual segments of the pilot member. The pilot member is retracted after the necking operation is completed to facilitate removal of the necked-in container from the tooling.
The pilot member is expanded by a rigid actuator which automatically pushes the segments into working position when the actuator is lifted. When the actuator is lowered, the pilot member is retracted by forces provided by four springs to each pilot member segment respectively.